In the preparation of molded aluminosilicates to form stable extrudates, granulates or moldings, useful as catalysts in chemical and petrochemical processes and as adsorbents in gas-purifying or separation processes, aluminum-containing binders or additives are frequently used. The extrudates, granulates or moldings, may be used in such processes as dewaxing, alkylation of aromatics, oligomerization of lower olefins, cracking, converting alcohols to fuels, and the like. However, this method does not work when molding high-silica or low alumina zeolites with special catalytic properties, e.g. very high stability, hydrophobicity, and shape selectivity (the combination of the molecular sieve effect and acid heterogeneous catalysis), such as found with zeolites of the pentasil group. Pentasils are a family of high-silica zeolites having ten-membered rings, which show largely five-ring building units in their structures. One well known type of pentasil is ZSM-5 (Zeolite Socony 5, tradename of Mobil Oil Corporation).
According to European Patent 0 102 544 (BASF), a silicic acid ester, such as tetramethyl orthosilicate is proposed as a binder or additive for fracture-resistant zeolite catalysts of the pentasil group. The strengthening action of this additive is based on a chemical reaction with the zeolite powder and therefore requires that the material used be matched accurately. Consequently, this method requires careful monitoring of the reaction to ensure that the proper amount of additive is present. Accordingly, the resultant molded pentasil zeolite is expensive and time-consuming to manufacture.
It is therefore desirable to provide a pentasil group zeolite catalyst which may be easily molded, extruded or granulated, easily and inexpensively, and which has high strength and abrasion resistance, and is highly fracture-resistant.